My invention relates to a method known from British Pat. No. 1,135,148 for operating a continuous process apparatus in which commodities packed in containers receive thermal treatment, wherein the containers by means of an endless conveyor, via a pressure resistant opening, are introduced into a treatment space and are traversed through a loop-shaped path in this space and hereinafter are again discharged therefrom via a pressure resistant outlet said method further comprising the injection of saturated steam at the desired treatment temperature into the treatment space for the heat transfer, whilst air is also introduced for maintaining the level of the desired overpressure in order to avoid a deformation of the containers, and finally on the upper side of the treatment space water is supplied at the desired treatment temperature.
In this known method a certain overpressure is maintained within the treatment space, said pressure being required to prevent the containers from being deformed as a consequence of the rise of the inner pressure. This so called "over-pressure" is obtained by feeding a non-condensable gas, preferably air which together with the supplied dripping water and the steam constitutes the treatment mixture within the space.
A steam-air mixture without the addition of water has the drawback that the transfer of heat by means of condensation of the steam is impaired by the presence of the air. When steam from the surroundings of the packed commodities condenses on the containers or on the carriers for the containers, the air rests more or less in those surroundings. This air constitutes therefore an insulating layer around the containers or carriers, whereby the admission of fresh steam is prevented or at least impeded.